The rod outer segment (ROS) disc membrane of the vertebrate eye has historically been one of the most important and intensively studied items in membrane biochemistry. This membrane structure is involved in the primary absorption of light photons and the initiation of the subsequent visual process. What is required is an understanding of the process whereby an absorbed photon leads to a nerve stimulation. This understanding must be sought at both a structural and biochemical level. Our research concentrates on the structural aspects. Because the structure of the ROS is pseudo-periodic, this membrane is suited to the X-ray diffraction technique. Knowledge of the structure is necessary in order to test or prove current hypotheses put forward to explain how photon absorption leads to neural stimulation. Efforts to date using X-ray film have been subject to artifacts and uncertainties because of the long time exposures required. Using the image intensification - computer controlled TV data acquisition and retrieval techniques that we have developed we will be able to obtain data in much shorter times. We have also developed suitable computer programs for analysis. The resolution permits the determination of the conformational changes upon bleaching, as well as some information concerning the orientation and extent of the protein in the disc.